The present invention relates to the field of angioplasty. In particular, the present invention is a two-piece guide wire assembly usable with a coaxially mountable dilatation balloon catheter.
Angioplasty has gained wide acceptance in recent years as an efficient and effective method for treating types of vascular diseases. In particular, angioplasty is widely used for opening stenosis in the coronary arteries, although it is also used for treatment of stenosis in other parts of the vascular system.
The most widely used form of angioplasty makes use of a dilatation catheter which has an inflatable balloon at its distal end. Using fluoroscopy, the physician guides the catheter through the vascular system until the balloon is positioned across the stenosis. The balloon is then inflated by supplying a fluid under pressure through an inflation lumen to the balloon. Inflation of the balloon causes stretching of the artery and pressing of the lesion into the artery wall to re-establish acceptable blood flow through the artery.
Over-the-wire catheters and fixed wire (i.e., non-over-the-wire) catheters are two types of dilatation catheters that are commonly used in angioplasty. An over-the-wire catheter has an inflation lumen and a guide wire through lumen through which a guide wire is advanced to establish a path through the stenosis. The separate dilatation catheter is then advanced over the guide wire until the balloon is positioned across the stenosis. The lumen for the guide wire must be sized with an inside diameter larger than the guide wire for easy wire movement. A fixed wire catheter has its own built in guide wire such that the guide wire, balloon and inflation lumen comprise a single unit.
Profile is a term used to designate the smallest opening a deflated, folded balloon of a dilatation catheter can traverse without damage to the catheter. Due to their "single unit" construction and no guide wire through lumen, fixed wire catheters generally have the advantage of having a smaller profile than over-the-wire catheters allowing fixed wire catheters to traverse smaller stenosis than over-the-wire catheters. However, separate guide wires as used with over-the-wire catheters are considered to be more steerable than fixed wire catheters due to being small in diameter.
Sometimes during the installation of a dilatation catheter (either over-the-wire or fixed wire), the balloon profile of the dilatation catheter is too large to cross the stenosis or the balloon inflated diameter is so small that the balloon cannot effectively dilate the stenosis. In other cases, the dilatation catheter may lack the control or flexibility necessary to track a path to the stenosis. In either situation, the catheter must be exchanged for one with a different size balloon or for one with different tracking characteristics to alleviate the respective difficulty.
To exchange an over-the-wire catheter, the guide wire must first be replaced by one 300 cm. long or the normal 175 cm. wire extended to 300 cm. by adding an extension wire to the proximal end of the guide wire located outside the patient's body. A typical balloon catheter is 135 cm. long. The dilatation catheter is then removed from the guide wire by holding the proximal end of the extended guide wire in place while pulling back on the catheter until the catheter is outside of the patient's body. By similar means a different catheter is placed on the guide wire and advanced to the area of the stenosis. The guide wire remains in position within the vascular system during the exchange of catheters such that the path to the stenosis need not be re-established. Not having to recross the lesion with a guide wire reduces the possibility of entering a false lumen.
To exchange a fixed wire catheter, the catheter within the patient's vascular system is removed and a different catheter is inserted in its place. This exchange of catheters necessarily requires removal of the built in guide wire portion of the catheter from the stenosis due to the "single unit" construction of the catheter and guide wire. Thus, to advance a fixed wire catheter to a stenosed area, the entire pathway through the vascular system must be re-established since no portion of the fixed wire catheter remains within the vascular system during the exchange. Establishing a path through the arterial tree to a stenosis is a difficult procedure and there is the potential of entering a false lumen. Thus, having to accomplish this task more than once is undesirable.
The profile of a dilatation catheter (either over-the-wire or fixed wire) dictates the minimum size of stenoses that are traversable by the catheter. The torqueability of a guide wire (whether separate or built in) determines the control necessary to maneuver and steer the guide wire or fixed wire catheter through the tortuous arterial paths within the vascular system. Both the guide wire and the fixed wire catheter have a distal spring tip that is formed in a bend such that torque applied to the proximal end of the guide wire or the fixed wire catheter is transmitted to the distal end for steering through the arterial branch vessels.
In the case of an over-the-wire catheter, if the diameter of the guide wire is below a nominal level, torque applied to the proximal end of the guide wire will only be partially transmitted through the length of the guide wire shaft to its distal end. This ineffective torque transmission results in a inability to adequately control the angular position of the guide wire distal tip. Thus, the nominal diameter of a guide wire shaft is partially determined by the requirement of being able to effectively transmit torque throughout the entire length of the guide wire shaft. For example, a 0.018" diameter guide wire is considered to be more torqueable than a 0.014" diameter guide wire.
In order to have the convenience of an over-the-wire catheter system and the lowest profiles, many over-the-wire catheter manufacturers have reduced the diameter of the guide wire through lumen so that only 0.014" diameter or smaller guide wires can be used. The guide wire lumen inside diameter is typically about 0.002" to 0.003" larger than the guide wire to allow for exchangeability and free wire movement of the catheter over the guide wire. Therefore, an over-the-wire catheter that is useable with a 0.014" diameter guide wire has a lower profile when compared to a similar catheter designed for use with a 0.018" diameter guide wire. However, the 0.014" diameter guide wire has the disadvantage of reduced guide wire torque control due to its smaller guide wire diameter when compared to the 0.018" diameter guide wire.
It is evident that there is a continuing need for improved over-the-wire catheter systems. In particular, there is a need for a catheter system that permits a reduction in the profile of over-the-wire dilatation catheters without sacrificing the guide wire torque control or torqueability level found in 0.018" or larger diameter guide wires. In addition, the catheter system should allow dilatation catheter exchangeability over the guide wire system.